When you're logged in, in the page source, there is a list called OrderedFriendsListInitialData.
According to rumour, it's a list of people that visit your profile the most, others say that it's a list of profiles you view the most, and yet other say it's the friends you interact with the most.
Can anyone shed some light on this by providing a definitive answer, or at least an educated one?

As You may notice it is initial data not chat list probably later chat script use this data to fill up people on list and make some extra check etc..

There is word ordered as well, Myself I'm not really active on facebook so have no way of checking it but it is known that fb analyses all Your steps and make this list based on thousands of factors to provide You with list of users You are likely to chat.

You father may be there because fb knows You are family and consider it as high possibility of conversation.

Well in the time passed since you first posted this they've changed the name of the list to InitialChatFriendsList which I suppose is a little more descriptive of what it is, but as far as how they determine what to put on there I think my friends and I have come up with a very plausible explanation.

When determining who you are most likely to communicate with on their chat system, facebook will obviously use a whole number of factors weighted differently to determine who you most want to talk to and who you most need to talk to.

the most important is who you actually talk to... who on fb chat that you communicate with most frequently will obviously show up on your chat list.

who you have public interactions w/ (i.e tagging in at some location, picture tagging, actual wall comments etc.)

Now those two are two very large factors when determining who they put on your list, beyond that it is a combination of who looks at your page and whose page you look at. Based on my list and the list of my friends, we determined that if you are inclined to look at somebody else's page/posts a lot and they are likely to do the same for you, they will move up in rank even if you don't have an actual interactions on facebook. A couple of people who I would admit to "stalking" the most on fb are not even on my list (at least not on the top 50 which is where i stopped checking) while other people who I do occasionally look at and I have reason to believe they would be looking at my profile as well are fairly high on my list (around 10-15th place). And of course there are the completely random individuals who show up on the list who probably are stalkers.

Anyways, my point is there are so many factors that determine who is going to be on this list, you really can't just attribute it all to people who stalk you and people you stalk. While in for some people that would be the case, for most of the people on the list there is a whole list of reasons they're on there.

Of course this is all based on a very small pool of data, so who knows...

I believe the first 3 are accurate. When I checked for myself, my boyfriend was one, and my two best friends were 2 & 3. Everything after that seems to be a bit random, because #4 was a person I haven't interacted with for years.